1. Field of the Invention
The present invention relates to a browser, and more specifically, to a browser equipped with the function to limit access to a restricted set of URLs. It also relates to data structures of supporting servers for servicing such browsers.
2. Description of the Related Art
A hypertext document is one which is linked to other documents via hyperlinks. A hyperlink often appears in a hypertext document as a piece of highlighted text. The text is usually a word or phase describing something of which a user might want further information. When the user activates the hyperlink, typically by clicking on it using a mouse, the user's view is changed so as to show the linked document, which typically contains more information on the highlighted word or phase concerned. Hyperlinks make it easy to follow cross-references between documents. Hypermedia documents are hypertext documents with multimedia capabilities. The regions on the screen which are active hyperlinks are called hot-links.
Nowadays, most people are familiar with the application of hypertext by using a mouse to click on hot-links on computer displays of homepages from the World Wide Web (the Web) on the Internet. Data on the Web is located via URLs. URL stands for "Uniform Resource Locator." It is a draft standard for specifying as object on the Internet. It specifies access method and the location for the files (Reference: http://www/w3/org/pub WWW/Addressing). Documents on the Web are written in a simple "markup language" called HTML, which stands for Hypertext Markup Language. File formats of data on the Web are specified as MIME formats; MIME stands for "Multipurpose Internet Mail Extensions." (Reference: http://www.oac.uci.edu/indiv/ehood/MIME/MIME.html). Examples of file formats on the Web are .au (probably the most common audio format), .html (HTML files), .jpg (JPEG encoded images), .mid (Midi music format), .mpg (MPEG encoded video), and .ps (postscript files).
Browsers are computer programs that make convenient the viewing and maneuvering of HTML documents on the web. The two most popular browsers are Netscape's Navigator (Reference: http://www.netscape.com) and Microsoft's Internet Explorer (Reference: http://www.microsoft.com/ie/default.esp). They provide a graphical user interface with standard point-and-click navigation methods. They support HTML files.
Hot objects in HTML files are each linked to a unique URL. Typical browsers allow users to attempt to access any URL. Sometimes browsers either employ, or are served by proxies which utilize, firewalls. Firewalls restrict access to certain URLs.
Often it is desirable to limit access to a relatively small set of URLs. Rather than specifying which URLs would not be accessible, as is done with firewalls, it is desirable to specify the small set of URLs. For example, an education program on a particular subject may want to keep the users focused on that specific subject. While firewalls may restrict access to undesirable sites, users can still meander to sites which are far from the subject. One implementation of the present invention has the browser list all accessible URLs. But this takes away from the browsing/searching experience. Therefore the present invention also provides the browser with the capability to allow searches of user-specified depth from the listed URLs. The invention further provides the browser with the capability of removing hot links from those pages which are at the maximum allowable depth from the listed URLs, so that users do not attempt to access these links only to receive a message that these links are not accessible.